This invention relates to improving the flow properties of wax-containing hydrocarbons. More particularly the present invention relates to pour depressants having utility in depressing hydrocarbon pour points where the hydrocarbon contains relatively high concentrations of paraffinic compounds, such as hydrotreated shale oil.
It is well known that petroleum oils often contain wax which will separate if the oil is cooled down below a certain temperature. As the temperature is lowered, the concentration of solid material increases, developing a gel caused by the formation of a coherent three dimensional network of wax crystals. As a result of this crystal structure, large amounts of oil are entrained in the crystal lattice of wax, thereby preventing the flow of the oil. The problem of wax formation is particularly significant in the treatment of highly paraffinic fuels, such as those derived from shale oil. Shale oil typically is hydrotreated to improve its generally poor storage stability. However, hydrotreating shale oil has been found to increase the wax or n-paraffin content of the shale oil from an already relatively high level. This results in a requirement that the hydrotreated shale oil be heated and kept above its pour point to avoid wax formation prior to and during processing. This further requirement increases the cost of transporting, storing and processing the shale oil.
The lowest temperature at which the oil will still flow is generally known as the pour point. When the fuel temperature goes below the pour point and the fuel is no longer free flowable, difficulty arises in transporting the fuel through flow lines and pumps, as for example, when attempting to transfer the fuel through pipelines.
This problem has been well recognized in the past and various additives have been suggested for depressing the pour point of oil. One function of such pour point depressants has been to change the nature of the crystals that precipitate from the oil, thereby reducing the tendency of the wax crystals to interlock and set into a gel.
U.S. Pat. No. 4,074,978 discloses the use of short chain unsaturated esters such as vinyl acetate, which can be copolymerized with long chain unsaturated esters such as dibehenyl fumarate. The copolymer may be admixed with asphaltenic material to produce a pour depressant having particular utility in depressing the pour point of atmospheric residuum and vacuum residuum. In Example I, the patentee discloses a series of tests in which a copolymer of behenyl fumarate and vinyl acetate are used in combination with an asphaltene to depress the pour point of the sample tested by 30.degree.-40.degree. F.
U.S. Pat. No. 3,532,618 discloses the use of asphaltenes from shale oil to depress the pour point of the shale oil.
U.S. Pat. No. 4,201,658 discloses the use of asphaltenic material for depressing the pour point of shale oil.
While each of the above-noted patents and publications discloses additives for reducing the pour point of hydrocarbons, such as shale oil, none of the publications discloses additives which permit the reduction of the pour point of the shale oil to a sufficiently low level to permit the shale oil, particularly hydrotreated shale oil, to be transported through pipelines without the use of an excessively large amount of pour depressant.
Accordingly, it would be desirable to provide a pour depressant which effectively reduces the pour point of oils having high wax contents by the addition of only relatively small quantities of additives.
It also would be desirable to provide a pour depressant which is relatively inexpensive.
It also is advantageous to employ a pour depressant which does not adversely affect the combustion properties of the resulting products.
The present invention is directed at a pour point depressant for a hydrocarbon comprising:
A. an asphaltene;
B. a copolymer of dibehenyl fumarate and vinyl acetate; and,
C. a copolymer of tallow fumarate and vinyl acetate.